Question

The salt of an oxyacid of a metal M contains one M, one sulphur and four oxygen atoms. The valency of metal M is
A. $0$
B. $2$
C. $3$
D. $4$

Answer 1

Hint: An oxyacid is a type of acid which consists of an oxygen atom bonded to a hydrogen atom and at least one other element than hydrogen and oxygen. The general structure of an oxyacid is $X - O - H$ and it dissociates into water to release protons and form respective anions of the acid. Most common examples are sulphuric acid, phosphoric acid, etc.

Complete answer:
As per question, it is given that the oxyacid consists of one metal M, one sulphur and four oxygen atoms. So, assume the formula of oxyacid is $MS{O_4}$.
As it is a neutral molecule, so the total valency of the compound is zero. Let the valency of the considered metal ion i.e., M be x. We know that the sulphur atom generally exists in its $ + 6$ valency and the oxygen atom usually form compounds with a valency of $ - 2$. Therefore, the valency of M can be calculated as follows:
$x + 6 + 4 \times ( - 2) = 0$
$ \Rightarrow x = + 2$
Hence it is a bivalent metal ion and has a valency of $ + 2$. So, option (B) is the correct answer.

Additional information-
As we know the valency of the metal atom, so we can determine the base formula of the oxyacid as follows:
Let the base formula of oxyacid is ${M_a}{(OH)_b}$. As it is a neutral molecule so overall valency is zero. Therefore, the relation between a and b can be calculated as follows:
$2a + b(1 - 2) = 0$
$ \Rightarrow 2a - b = 0$
$ \Rightarrow b = 2a$
Substituting the value of b in the formula assumed:
$ \Rightarrow {M_a}{(OH)_{2a}}$
Hence, the base formula of the oxyacid is $M{(OH)_2}$.

Note:
It is important to note that ketones and oxocarboxylic acids are sometimes also referred to as oxyacids. Also, the dissociation of an oxyacid depends upon the electronegativity of the X atom considered. If X is strongly electronegative, then it will dissociate to give protons whereas if it has low electronegativity, then the acid will dissociate to give hydroxide ions.